Polymers that have long-chain branching (LCB), i.e., long enough to result in entanglement, have qualitatively different flow behavior than polymers that are purely linear. LCB profoundly affects the processing and crystallization of the branched polymers. As such, it is often desirable to design polymers with an optimal amount and type of LCB to achieve a particular set of processing characteristics and physical properties.
Some conventional forms of polyethylene, such as LDPE produced by high pressure free radical processes, contain a broad mix of LCB. More recently, other forms of polyethylene produced using metallocenes and other single-site coordination catalysts have a variety of different types of LCB. However, most polyethylenes with LCB are only one generation away from the linear backbone and have very limited branch density. The effectiveness of those polyethylenes with LCB in use as additives in modifying the flow properties of polyethylene without LCB has been limited.
Polyethylenes having a high degree of branching, such as dendritic or multi-generation, branch-on-branch polymers might be particularly useful as additives in modifying the flow properties of non-LCB polyethylenes. However, synthesis of such highly branched polyethylenes is typically laborious and expensive.
It would be desirable to have a useful, inexpensive additive that would have a significant impact on the processing and performance balance of conventional polymers, particularly polyethylenes such as LDPE.